Horizontal centrifugal separator

ABSTRACT

A horizontal centrifugal separator is provided in which the hermeticity of the casing can be improved by using sealing means having a simple structure. 
     The horizontal centrifugal separator is configured such that a groove formed along a joint surface between an upper casing and a lower casing constituting the casing is outwardly bent near an opening of the casing, and that an elastic sealing member is disposed in the groove and an end portion thereof abuts against a sealing surface provided on a ring member which is provided so as to surround the outer circumference of the opening of the casing and is pressed against the casing. In this case, surface sealing is constituted by the end portion of the elastic sealing member and the sealing surface of the ring member. In this manner, the hermeticity can be improved without using a sealing member having a complicated structure.

TECHNICAL FIELD

The present invention relates to a horizontal centrifugal separatorincluding a rotary bowl and a screw conveyor inserted into the rotarybowl. In particular, the invention relates to a horizontal centrifugalseparator including sealing means that, while having a simple structure,can improve the hermeticity of a casing containing the rotary bowl andthe screw conveyor.

BACKGROUND ART

A horizontal centrifugal separator referred to as a decanter is one typeof known solid-liquid separator that uses centrifugal force. Forexample, as shown in FIG. 1, a decanter 1 has a basic structure in whicha rotary bowl 11 rotatable about its horizontal axis and a screwconveyor 12 inserted into the rotary bowl 11 are contained in a casing 2serving as an exterior casing. The casing 2 is separated into a lowercasing 21 having a solids outlet 21 a and a separated-liquids outlet 21b formed in the lower part thereof and an upper casing 22 detachablefrom the lower casing 21. The lower casing 21 and the upper casing 22have flanges 23 formed along the respective opening edges thereof. Thecasing 2 having a substantially cylindrical shape is formed by securingthe flanges 23 to each other with securing means 24 such as bolts.

Openings 25 having, for example, a circular shape are formed in theopposite end faces of the casing 2, and the rotary shafts of the rotarybowl 11 and the screw conveyor 12 extend through the openings 25 and arerotatably supported by bearing means 13. Mechanical seal housings 14 forsealing the rotary shafts are disposed in the openings 25, and O-rings15 provided on the outer circumferences of the mechanical seal housings14 hermetically seal the gaps between the mechanical seal housings 14and the openings 25.

The barrel portion of the rotary bowl 11 is composed of three portions,i.e., a cylindrical portion on a first end side thereof, an intermediateconical portion, and a circular portion on a second end side. Theportion formed into a conical shape forms a beach portion in whichsolids conveyed by the screw conveyor 12 are separated from liquids andare thereby dewatered. The cylindrical portion on the first end sideforms a screen portion for washing the dewatered solids with washingwater, and the washed solids are discharged through solids outlets 16.The cylindrical portion on the second end side forms a pool (fluid pool)portion for reserving a feed fluid supplied to the inside of the rotarybowl 11 and has separated-liquids outlets 17 formed in the end facethereof. A screw vane 18 and feed fluid supply ports 19 are formed inthe barrel portion of the screw conveyor 12 inserted into the rotarybowl 11, the feed fluid supply port 19 being provided for supplying thefeed fluid fed from a feed fluid supply nozzle 3 to the rotary bowl 11through the action of centrifugal force.

In the structure described above, by transmitting the power of a motor32 serving as a driving mechanism to a pulley 33 through a rotary belt31, the rotary bowl 11 is rotated at a predetermined rotation speed.When the feed fluid is supplied to the pool portion while the rotarybowl 11 is rotated, the solids are settled out through the action of thecentrifugal force. The solids are conveyed to the beach portion by thescrew conveyor 12 rotated through a gearbox 34 used as a differentialspeed generating mechanism and are then dewatered. The dewatered solidsare then washed with washing water from washing water injection ports 35when they pass through the screen portion. The washing drainage used forwashing the solids is discharged through discharge holes 36 formed inthe screen portion. The solids having been washed in the screen portionare discharged from the solids outlets 16 and are then discharged to theoutside of the separator through the solids outlet 21 a. The liquidsseparated from the solids (separated liquids) are discharged from theseparated-liquids discharge outlets 17 and are then discharged to theoutside of the separator through the separated liquids outlet 21 b. FIG.1 shows the decanter of the screen bowl type. However, decanters of thesolid bowl type that do not have the screen portion are also widelyknown.

As described in, for example, patent documents such as Japanese PatentApplication Laid-Open No. 2007-44671, a number of studies havepreviously been conducted to improve the sealing properties ofmechanical seals. However, only a few studies have been made to ensurethe hermeticity between the mechanical seal housing 14 and the casing 2,which are non-rotating mechanisms. If the set pressure is increased,leakage can occur between the mechanical seal housing 14 and the casing2. Therefore, in horizontal decanters having a casing structure composedof two separated (upper and lower) casings, the internal pressurethereof during use is limited to several tens kPa or less. At present,when the internal pressure reaches a higher level, the treatment isperformed using decanters having an integral cylindrical structure orvertical decanters. However, in decanters having an integral cylindricalstructure, the rotary members must be pulled out in the axial directionthereof when disassembled. Therefore, such decanters have drawbacks inthat the assembling-disassembling process is complicated and that asufficiently large space must be provided for maintenance. Inparticular, decanters of the screen bowl type in which the ratio betweenthe diameter and length of the bowl is large have an influence on thesize of buildings. Accordingly, the integral cylindrical structure hasnot practically been used in such decanters.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

With reference to FIG. 2, the structure of the portion from whichleakage occurs is described, in order to elucidate the cause of theleakage. Specifically, as shown in FIG. 2, a groove 27 is formed in anend surface 26 of the lower casing 21, and an O-ring 28 used as asealing member is disposed in the groove 27, whereby the joint surfacebetween the lower casing 21 and the upper casing 22 is sealed. However,since the opening 25 for allowing the rotary shafts to pass therethroughis formed in the lower casing 21, the O-ring 28 cannot be provided overthe entire circumference of the lower casing 21, and the O-ring 28 isdiscontinuous at the opening 25. In this sealing structure, the end ofthe O-ring 28 is in point contact with the O-ring 15 of the mechanicalseal housing 14, and therefore the hermeticity is low. Moreover, theO-ring 28 is contracted when the separator is operated under, forexample, a reduced pressure condition. In such a case, a gap is formedbetween the O-ring 28 and the O-ring 15, and this results in a furtherincrease in the amount of leakage.

Moreover, in the structure shown in FIG. 2, the O-ring 15 of themechanical seal housing 14 can be caught between the upper casing 22 andthe lower casing 21 when the upper casing 22 is placed on the lowercasing 21, for example, at the time of assembly of the separator orafter the maintenance. In such a case, the O-ring 15 is deformed, andthis causes a problem in that the hermeticity is reduced. In addition,in this structure, the assembling and maintenance operations are “blind”operations in which whether or not the O-ring 15 is caught cannot bevisually determined. Therefore, disadvantageously, the point of leakageis not easily determined, and the workability is low.

As described above, the horizontal decanter 1 has a drawback in that thehermeticity is low but has advantages in that its structure is simplerand the cost is lower than those of vertical decanters. Therefore, thereis a demand for a horizontal decanter to overcome the problem ofhermeticity. However, as the sealing structure becomes complicated, theabove advantages of the horizontal decanter 1 are reduced. Therefore,the sealing structure must be as simple as possible. The advantages ofthe structure of the inventive decanter against the integral cylindricalstructure will be described later.

The present invention has been made in view of the above circumstances,and it is an object of the invention to provide a horizontal centrifugalseparator in which the hermeticity of a casing is improved by usingsealing means having a simple structure.

It is another object of the invention to provide a horizontalcentrifugal separator including sealing means configured such that anO-ring of a mechanical seal housing is prevented from being caughtbetween an upper casing and a lower casing when the upper casing isplaced on the lower casing.

Means for Solving the Problems

A horizontal centrifugal separator of the present invention includes: arotary bowl; a screw conveyor that is inserted into the rotary bowl; acasing that contains the rotary bowl and the screw conveyor; and bearingmeans for supporting a rotary shaft of the rotary bowl that extendsthrough an opening of the casing. The horizontal centrifugal separatorfurther includes sealing means for hermetically sealing the casing byproviding a groove formed along a joint surface between an upper casingand a lower casing constituting the casing so as to be outwardly bentnear the opening thereof, and disposing an elastic sealing member in thegroove such that an end of the elastic sealing member abuts against asealing surface provided on a ring member, the ring member beingprovided so as to surround an outer circumference of the opening andbeing pressed against the casing.

The elastic sealing member may include: a block member having an endthat abuts against the sealing surface; and a linear member having anend that engages with a recess formed in the other end of the blockmember.

The ring member may be a flange portion of a bushing that is fitted,from an axially outward side of the opening, in a gap between theopening of the casing and a mechanical seal housing for sealing therotary shaft disposed in the opening of the casing. The sealing surfacemay be configured to be a surface of a gasket sandwiched between theflange portion and a surface of the casing.

EFFECTS OF THE INVENTION

The present invention employs the structure in which surface sealing isformed as follows. Specifically, the groove formed along the jointsurface between the upper casing and the lower casing constituting thecasing is provided so as to be outwardly bent near the opening. Then,the elastic sealing member is disposed in the groove such that the endof the elastic sealing member abuts against the sealing surface providedon the ring member, the ring member being provided so as to surround theouter circumference of the opening and being pressed against the casing.In this manner, the hermeticity can be improved without using sealingmeans having a complicated structure.

In addition, the present invention employs the structure furtherincluding the bushing that is fitted, from the axially outward side ofthe opening, in the gap between the opening of the casing and themechanical seal housing disposed in the opening of the casing. In thismanner, the O-ring of the mechanical seal housing can be prevented frombeing caught between the upper casing and the lower casing when theupper casing is placed on the lower casing. Therefore, a reduction inhermeticity caused by the deformation of the O-ring can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view illustrating the wholestructure of a horizontal decanter.

FIG. 2 shows a conventional sealing structure.

FIG. 3 shows a sealing structure according to an embodiment of thepresent invention.

FIG. 4 shows the sealing structure according to the embodiment of thepresent invention.

FIG. 5 shows a modified example of the sealing structure according tothe embodiment of the present invention.

FIG. 6 shows another modified example of the sealing structure accordingto the embodiment of the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

-   -   11 rotary bowl    -   12 screw conveyor    -   2 casing    -   21 lower casing    -   22 upper casing    -   28 O-ring    -   4 bushing    -   42 flange portion    -   44 gasket

BEST MODES FOR CARRYING OUT THE INVENTION

A horizontal centrifugal separator according to a preferred embodimentof the present invention will be described in detail with reference tothe accompanying drawings. The basic structure of the horizontalcentrifugal separator of the present embodiment is the same as thestructure shown in FIG. 1, and a detailed description thereof will beomitted.

As shown in FIGS. 3 and 4, in the horizontal centrifugal separator ofthe present embodiment, a groove 27 in which an O-ring (linear member)28 serving as an elastic sealing member is disposed is bent outwardlynear the opening 25 such that an end portion of the O-ring 28 is exposedoutward. The end portion of the O-ring 28 may be flush with the surfaceof the casing or may protrude slightly from the surface of the casing.

The horizontal centrifugal separator further includes a bushing 4 fittedin the gap between the opening 25 and the mechanical seal housing 14.The bushing 4 includes: a tubular portion 41 that is fitted in the gap;and a flange portion 42 serving as a ring member formed in the outercircumference of the tubular portion 41, and is pressed against thecasing 2 using securing means 43 such as a bolt. In this case, it isconfigured such that the end portion of the O-ring 28 abuts against asurface of a gasket 44 interposed between the flange portion 42 and thecasing 2.

When the separator having the above structure is assembled, first theO-ring 28 is disposed in the groove 27. After the position of themechanical seal housing 14 is adjusted, the upper casing 22 is placed.Then, the bushing 4 is caused to slide in the axial direction to fit thetubular portion 41 in the gap, and the flange portion 42 is pressedagainst the casing 2 using the securing means 43. In this manner, theend portion of the O-ring 28 abuts against the gasket 44, wherebysealing is formed.

Specifically, the sealing means of the present embodiment providessealing which is constituted by the outwardly bent O-ring 28 and thegasket 44 provided in the bushing 4 in place of the conventionalstructure in which the sealing is constituted by the O-ring 28 on thecasing side and the O-ring 15 of the mechanical seal housing 14.Therefore, according to the present embodiment, surface sealing usingthe surface of the gasket 44 is provided. Hence, the hermeticity can befurther improved as compared to the conventional point contact sealing.Moreover, no significant modification is made to the conventionalsealing structure, and therefore the hermeticity can be improved using asimple structure. In other words, the problem of hermeticity is overcomewithout sacrificing the advantages of low-cost horizontal decantershaving a simple structure.

Moreover, the present embodiment employs the structure that furtherincludes the bushing 4 fitted, from the axially outward side, in the gapbetween the opening 25 of the casing 2 and the mechanical seal housing14. In this manner, the O-ring 15 of the mechanical seal housing 14 isprevented from being caught between the upper casing 22 and the lowercasing 21 when the upper casing 22 is placed on the lower casing 21.Therefore, a reduction in hermeticity caused by the deformation of theO-ring 15 can be prevented.

Furthermore, in the present embodiment, the sealing area between theO-ring 28 and the gasket 44 is easily observed and inspected. Therefore,even when a change in pressure is found in a hermetic test, it is easilydetermined whether or not the leakage occurs in the sealing area. Inother words, advantageously, the point of leakage is easily determinedand fixed.

Moreover, in a modified example of the elastic sealing member, a blockmember 5 shown in, for example, FIG. 5 may be provided. Specifically, inthis structure, the block member 5 is fitted in the groove 27 from thebent portion to the end portion thereof. As in the O-ring, one endportion of the block member 5 may be flush with the surface of thecasing or may protrude slightly from the surface of the casing. Theblock member 5 has a recess 51 formed in the other end portion thereof,and the end portion of the O-ring 28 is engaged with the inside of therecess 51. The O-ring 28 may be bonded or not be bonded to the recess 51to form the engagement between the O-ring 28 and the recess 51.Preferably, the O-ring 28 and the recess 51 are not bonded to each otherwhen an appropriate bonding agent is not found for the engagement shape,or since the O-ring 28 and the recess 51 are difficult to reuse whenbonded to each other. Even in such a structure, the same effects asthose in the above embodiment can be obtained, and the hermeticity canbe reliably improved by providing the block member 5 serving as anelastic sealing member. The shape of the block member 5 is not limitedto the shape shown in FIG. 5, and the shape may be changedappropriately. For example, the shape shown in FIG. 6 may be used as amodified example.

In the above embodiment, the sealing member disposed in the groove 27 isnot limited to the O-ring 28 having a circular cross-section. Any linearmember may be used so long as it can be disposed in the groove 27. Forexample, a sealing member having a rectangular cross-section or othercross-section may be used.

The sealing surface against which the end of the elastic sealing memberabuts is not limited to the surface of the gasket 44 of the bushing 4and may be a surface of a sealing member other than the gasket 44.Alternatively, the sealing surface may be formed by applying RTV (RoomTemperature Valcanizing) rubber. The ring member on which the sealingsurface is provided is not limited to the flange portion 42 of thebushing 4 and may be other ring members.

It is needless to say that the application of the decanter is notlimited. The decanter can be used for separation of various materialsinto solids and liquids and for selection of, for example, wasteplastic.

While the present invention has been described with reference to thespecific embodiments, it is apparent to those having ordinary knowledgein the art that various modifications can be made so long as they do notdepart from the scope of the present invention. Accordingly, thetechnical scope of the present invention is not limited to theabove-described embodiments but must be defined by the claims or theequivalence thereof.

Example

A hermeticity test was actually performed using the sealing means havingthe structure shown in FIG. 5. An example of the results is describedbelow.

(Test Conditions)

O-ring Cross Section Dia.: 11 mm, Durometer: 50

Groove Depth: 8 mm

Rubber Ring Gasket Durometer: 60

Block Durometer: 70

Pressure (kg/cm²): 0.35, 1.0, 1.25, 1.5

Retention time: 10 to 20 min

(Test Results)

Leakage was not found at all the pressures listed above. In other word,sufficient hermeticity was confirmed in the present invention.

1. A horizontal centrifugal separator comprising: a rotary bowl; a screwconveyor that is inserted into the rotary bowl; a casing that containsthe rotary bowl and the screw conveyor; and bearing means for supportinga rotary shaft of the rotary bowl that extends through an opening of thecasing, the horizontal centrifugal separator characterized by furthercomprising sealing means for hermetically sealing the casing byproviding a groove formed along a joint surface between an upper casingand a lower casing constituting the casing so as to be outwardly bentnear the opening thereof, and disposing an elastic sealing member in thegroove such that an end of the elastic sealing member abuts against asealing surface provided on a ring member, the ring member beingprovided so as to surround an outer circumference of the opening andbeing pressed against the casing.
 2. The horizontal centrifugalseparator according to claim 1, wherein the elastic sealing memberincludes: a block member having an end that abuts against the sealingsurface; and a linear member having an end that engages with a recessformed in the other end of the block member.
 3. The horizontalcentrifugal separator according to claim 1, wherein: the ring member isa flange portion of a bushing that is fitted, from an axially outwardside of the opening, in a gap between the opening of the casing and amechanical seal housing for sealing the rotary shaft disposed in theopening of the casing; and the sealing surface is a surface of a gasketsandwiched between the flange portion and a surface of the casing. 4.The horizontal centrifugal separator according to claim 2, wherein: thering member is a flange portion of a bushing that is fitted, from anaxially outward side of the opening, in a gap between the opening of thecasing and a mechanical seal housing for sealing the rotary shaftdisposed in the opening of the casing; and the sealing surface is asurface of a gasket sandwiched between the flange portion and a surfaceof the casing.